Synchronizing system



April 29, 1947. M. GABRIEL ETAL 2,419,637

SYNCHRONIZ ING SYSTEM mmvron HARCEL mama 4 WWW GUANELLA 1! fla ATTORNEYf April 29, 1947. GABR|EL ETAL 2,419,637

smcrmomzms SYSTEM Filed Sept. 8, 1944 3 Sheets-Sheet 3 AMPLIFIERINVENTOR. HARCEL GABRI'EL 4 GUSTAV cum ELLA ATTORNEY Patented Apr. 29,1947 SYNCHRONIZING SYSTEM and Gustav Guanella, assignors to Radio Pat-Marcel Gabriel, Biel, Zurich, Switzerland,

ents Corporation, tion of New York Application September 8,

In Switzerland Fe New York, N. Y., a corpora- 1944, Serial No. 553,140bruary 20, 1943 14 Claims. (01. 172 253) The present invention relatesto a system for and method of synchronizing periodic phenomena ordevices, such as rotating machines, and the main object of the inventionis to provide an improved system of this type which is both simple indesign as well as eflicient and reliable in operation.

It is known to synchronize rotating machines by comparing alternatingvoltages having frequencies proportional to the speeds of rotation ofsaid machines, more particularly by determining the frequency and phasedeviations between said voltages and readjusting the relative speed ofthe machine to be synchronized so as to restore proper frequency andphase coincidence. A disadvantage of this method is the fact that'apermanent difference may exist between the frequency responsecharacteristics of the machines to be synchronized, which difference mayamount to an integer multiple of the oscillation period of thealternating voltages being compared. For this reason, additional costlymeans have often to be provided to avoid differences in the frequencyresponse characteristics.

It is also known to synchronize two machines by comparing the phase ofsynchronizing impulses derived from one of the machines (synchronizingmachine) with the phase of the other machine (machine to besynchronized). This may be accomplished by reversing the polarity of thesynchronizing signals in rhythm with the rotation of the machine,whereby to obtain a regulating quantity from the resulting voltages andcurrents which may serve to influence or control the machine to besynchronized so as to reduce its deviation from synchronism. Thedisadvantage of thismethod is due, among others, to the fact that arelatively wide band frequency channel is required for the transmissionof the synchronizing impulses.

The disadvantages of the known synchronizing 7.

methods are overcome according to the present invention by the use ofalternating currents or voltages of periodically varying frequency beingproduced by both the synchronizing machine and the machine to besynchronized, the difference frequency between said currents or voltagesbeing determined and utilized to control the speed of the machine to besynchronized so as to restore and maintain it in locked synchronism withthe synchronizing machine.

The invention as to its objects and novel aspects will be furtherunderstood from the following detailed description of a few practicalembodiments thereof, taken in reference to the accompanying of time,according to drawings forming part of the specification, and

wherein:

Figure 1 is aschematic block diagram of a basic synchronizing systemconstructed in accordance with the principles of the invention;

gram illustrating modifications of the system shown in Figure 5;

Figure 7 is a diagram of a synchronizing system showing anothermodification of Figure 5; and

Figures 8a and 8b are block diagrams similar to Figure 1, illustratingstill further modifications of the invention.

Referring more particularly to Figure )1, item M1 indicatesschematically the synchronizing machine or other rotating device anditem M: indicates the machine to be synchronized. Items W1, W: are 'apair of alternating current voltage generators each coupled with one ofthe machines M1 and M2 and serving to produce alternating currentenergies having frequencies f1 and f2, respectively. Item R is amodulator in which the frequencies f1 and f: are mutuallyintermodulated, and item Z is a device to produce a control current fromthe modulation product suitable to cause the speed of machine M2 to beregulated. Before the machines are actually synchronized, it isnecessary that their speeds should be caused to coincide approximatelyby known means, so that there are only relatively small deviationsbetween the instantaneous frequencies f1 and f2.

Figure 2 shows more clearly the periodic variations of the frequenciesf1 and f: as a function one embodiment of the invention. The period T1of frequency f1 corresponds to a. single rotation of the shaft of thesynchronizing machine M1 and the period of frequency T2 corresponds to asingle rotation'of the machine M2 to be synchronized. Both frequenciesf1 and f2 furthermore change their value gradually within the samefrequency range between predetermined lower and upper limit frequencies.At the beginning of the synchronization process, there is a displacement'1 between the alternating currents or voltages to be compared,resulting in the difference frequencies Fa and Fb, as indicated in thedrawing. In the' nc his to be 2 sense from Pe of...

speed of revolution of the at "1 1'2 Figure n various manwell lllOWl'lmagnetic 3 devices M1 and M2 3. having peripheral y magnet provided ter.an alternating c to the periodic flux 7 is variable reluctance g betweensuccessive gradually r tone I and each voltage W1 2 variations when a toteeth is o": varying Anothe forated c machines M ing a beam or cell. var

en by the periodica ly interrupted upon a photoelectric ch or spacingdistance between succes b perforations, the frequency of the outputcurrent of the photoelectric cell may be given a desired variationincluding a linear or saw-tooth-liire change, as shown in Figure 2.

The synchronizing process according to the invention may be furtherunderstood by reference to Figures 3a and 31), wherein the shaded areaspresent an approximate picture of the control voltage during thecorresponding time periods. The period T2 of the alternating voltageproduced by the generator W2, at the beginning of the synchronizingprocess, is shown to be greater than the period T1 of the voltageproduced by generator W1, in accordance with the assumption of aninitially lower speed of the machine M: to be synchronized. After thedisplacement T between the machines M1 and Me has been reduced to aminimum by reducing the difference between the frequencies f1 and is,further synchronizing or regulation to a definite relative phase willoccur by the interaction of the alternating voltages in the modulator R.In the latter case, the'direct current component of the control voltageK which occurs after the frequencies f1 and f2 have been brought toconcidence, constitutes a further regulating quantity which varies bothas to magnitude and sign, depending upon the sense of relative phasedeparture from a normal phase relation between the frequencies f1 andin. More particularly, this-control voltage will be zero if the relativephase displacement between the equalized frequencies f1 and I2 is 90.The regulating device of the machine M: is then no longer influenced,that is to say, at this instant an entirely rigid or locked synchronismis maintained between thetwo machines. If small deviations from thisnormal phase position occur in either sense, the direct control currentproduced by the modulator R will attain relatively high values ofcorresponding sign, so as to cause the phase to be readjustedimmediately in the desired direction, to restore the synchronism betweenthe devices.

As already mentioned, with such an arrangement, the control voltage orcurrent K derived from the frequencies f1 and is can only be em ployedfor synchronizing from one side, that is to say, only if the initialspeed or the machine to be synchronized differs from that of thesynchronizing machine in a predetermined sense. If, however, instead ofregulat n to frequency difference equal to zero, the i gulation is for aconstant mean frequency difference, it is possible to synchronize fromboth sides or for either sense of deviation of the speed of machine M2from a desired normal difference therebetween and the speed of machineM1.

Bilateral synchronization may also be achieved by comparing multi-phasevoltages with a periodically varying frequency, whereby a resultantfield is produced which rotates in accordance with the difference of thefrequencies 1 and f2. This rotating field revolves either in a clockwiseor counterclockwise direction depending upon the sense of deviation fromsynchronism, i. e., in turn the sense of the frequency difference, sothat a correct regulation is enabled under all circumstances. Thismethod may, for instance, be carried out by the aid of a rotatingfieldmachine whose rotor revolves at a speed proportional of the differenceof the frequences f1 and f2, or according to the known multi-phasemodulation method. With the latter method, a rotating field is obtainedin the output system whose frequency of rotation is equal to thealgebraic sum of the frequencies of the associated input rotatingfields.

Synchronization to a constant frequency difference will be furtherunderstood by reference to the diagram shown in Figure 4, wherein f1 andf2 again represent the frequencies of the alternating voltages which inthis case rise and fall steadily within two different frequency rangesand are again produced by the generators W1 and W2 coupled with themachines Ml and M2, respectively In the beginning, there is adisplacement T between the two frequencies f1 and f2, resulting in thetwo frequency diff :ences Fa and Fb. The speed of the machine M2 to besynchronized is now regulated until the constant mean frequencydifference F0 prevailing with a minimum phase displacement T is reached..Contraryto the first method described, the regulating current obtainedby frequency modulation and subsequent filtering of the modulationproduct assumes a definite constant frequency value when both machinesare in synchronism.

The method according to the invention may be realized in practice bymeans of the arrangement shown in Figure 5. The machines M). and M2 areshown to drive tone wheels or alternating current generators W1, W2having irregular tooth pitches so as to obtain a frequency deviation ofthe type shown in Figures 2 or 4. The frequencies f1 and 12 thusproduced in the induction coils S1 and s; are mutually intermodulated inthe rec- Fb, only the lower one Fa is passed by the lowpass filter TP. Adirect currentvoltage E proportional to the frequency difference Fa isthen produced in the frequency discriminator Z. This voltage, afteradequateamplification in an amplifier V, serves to operate anelectromagnetic brake B affecting the speed of the machine m. Thediscriminator Z may be designed as shown in Figures 6a and 6b, Whenregulating to zero frequency difference, a discriminator or simple slopefilter according to Figure 6a may be used. On the other hand, if thesynchronization is to a certain frequency difference F0, according tothe example described in connection with Figure 4, a discriminator asshown in Figure 6b is required which contains a band filter tuned to thefrequency F0 and serving as a phase or frequency discriminator elementin a manner well known in the art. Accordingly, with input frequenciesabove or below the valueFo, the discriminator produces a positive ornegative control voltage applied to the amplifier V. In this manner, astable regulation of the machine M2 to a constant frequency differenceand phase with respect to I the machine M1 is enabled in a most simplemanner.

When comparing multi-phase voltages, the arrangement shown in Figure 7may be used. The three-phase modulator R produces three-phase voltageswith frequencies Fa and Pb, three-phase low-pass filter TP beingprovided to pass only the alternating voltage of frequencies Fa. The

-latter, after amplification in the amplifier V,

serves to drive a synchronous motor A which in turn serves to actuate aregulating element 0 in .the form of a resistance as shown,

To obtain a three-phase voltage from the generators W1 and W2, thelatter may consist of three tone wheels relatively displaced by 120electrical degrees and having their output windings connected in star ordelta to obtain a concatenated .three-phase output applied to thethree-phase modulator R. The latter may consist of three electronicmixer tubes havin their cathodes connected to the common neutral point,being each provided with two control grids excited by the correspondingphase voltages supplied by the generators W1 and W2, respectively.

The plates of the tubes will then supply the corresponding combinationfrequencies Fa and Fb applied to the low-pass filter TP. Accordingly,the output of the filter TP, upon amplification by the amplifier V,supplies a three-phase current having a frequency Fa which varies inproportion to the degree of deviation of the device M2 to besynchronized from synchronism with the synchronizing device M1. Thiscurrent when applied to the three-phase asynchronous motor A producestherein a rotating field having a speed which varies in proportion tothe deviation from synchronism between the device M1 and NIz and whosedirection of rotation depends upon the sense of said deviation inrelation to the sense of rotation of the synchronizing device M1.

In an arrangement according to Figure 5, additional means may beemployed to insure exact synchronism between the synchronizing machineand the machine to be synchronized, Thus, in the arrangement accordingto Figure 8a, the modulator R0 serves to maintain the synchronism, whilea further comparison device R1 comes into operation after the generatorsW; and We have attained the same frequency due to the effect of thelow-pass filter TPi connected between the output of R1 and the controlmember of the machine M2. The comparison device R1 may, for

instance, operate according to the wattmeter principle and supply itsregulating voltage until its input voltages are phase displaced by or,When using a series phase-displacing element P in one of its inputcircuits, until the generators W1 and W2 supply voltages which are inexact phase with each other.

In the arrangement shown in Figure 8b, the comparison devices R0 and R1are united in a single comparison device R and the segregation of tworegulating voltages is effected outside this device. In this manner, apair of control currents are produced in Figures 8a and 8b, one of whichis responsive to relative frequency deviations between the synchronizingenergies, while the other varies in sense and magnitude in accordancewith the relative phase between said energies, after their frequencieshave been equalized by said first control current.

Instead of employing a saw-toothed-shaped frequency variation curvedescribed hereinabove for the alternating voltages being compared, it isalso possible to use a sinusoidal or any other type of frequencyvariation. The modulation periods T1, T2 may also correspond to morethan one revolution of the shaft of thesynchronizing machine or machinesto be synchronized, respectively. It is also possible to pass thecontrol voltage K obtained by filtering the modulation product to anindicating instrument and to regulate manually the speed of the machineM2 to be synchronized.

In addition to producing a frequency difference in a purely electricalmanner by the formation of a product in a modulator, it is also possibleto derive the frequency difference in a purely mechanical manner byoperating the Wheels of a mechanical differential at the frequencies ofthe alternating voltages to be compared, in which case the transmissionwheel of the differential rotates with the frequency difference. The frequencies may also produce two rotating fields with different speeds ofrotation in an electrical differential whose rotor revolves with thedifference of the frequencies.

In practice, it may happen that the difference T in the frequencyresponse curves cannot be reduced to the desired extent because thefrequency difference may be already below the controllable valuesbeforethe desired end state is reached. This can be remedied by increasing thefrequencies f1 and f2.

The method according to the invention may also be used for synchronizingany kind of oscillation generator, in which case the control orcorrecting voltage or other quantity serves to adjust the frequency ofthe generator to be synchronized in accordance with any of the wellknown means available for this purpose in the prior art. 1

We claim:

1. Means for synchronizing two periodic phenomena comprising means forproducing a pair of alternating current electric energies each having afrequency varying periodically in a definite integral relation to theperiodicity of a different one of said phenomena, means for mutuallyintermodulating said energies to produce difference frequency energy,and further means for utilizing said difference frequency energy toaffect at least one of said phenomena, whereby to restore and maintainthe synchronism between said phenomena.

2. Means for synchronizing two periodic phenomena comprising means forproducing a pair of alternating current electric energies each having afrequency varying periodically within each period of a different one ofsaid phenomena, means for mutually intermodulating said energies toproduce difference frequency energy, and further means for utilizingsaid difference frequency energy to affect at least one of saidphenomena, whereby to restore and maintain the synchronism between saidphenomena.

3. Means for synchronizing two periodic phenomena comprising means forproducing a pair of alternating current electric energies each having afrequency varying linearly and periodically between lower and upperlimits and in definite integral relation to the periodicity of adifferent one of said phenomena, means for mutually intermodulating saidenergies to produce difference frequency ing said difference frequencyenergy to affect at least one of said phenomena, whereby to restore andmaintain the synchronism between said phenomena.

4. Means for synchronizing two periodic phenomena comprising means forproducing a pair of alternating current electric energies each having afrequency varying linearly and periodically between equal lower andupper limits within each period of a different one of said phenomena,means for mutually intermodulating said energies to produce differencefrequency energy, and further means for utilizing said differencefrequency energy to affect at least one of said phenomena, whereby torestore and maintain the synchronism between both said phenomena.

5. Means for synchronizing two periodic phenomena comprising means forproducing a pair of alternating current electric energies each having afrequency varying linearly and periodically between different lower andupper limits within each period of a different one of said phenomena,means for mutually intermodulating said energies to produce differencefrequency energy, and further means for utilizing said differencefrequency energy to affect at least one of said phenomena, whereby torestore and maintain the synchronism between both said phenomena.

6. Means for synchronizing two periodic phenomena comprising means forproducing a pair of alternating current electric energies each having afrequency varying linearly and periodically according to a saw-toothcurve between equal lower and upper limits and within each period of adifferent one of said phenomena, means for mutually intermodulating saidenergies to produc difference frequency energy, and further means forutilizing said difference frequency energy to affeet at least one ofsaid phenomena, whereby to restore and maintain the synchronism betweensaid phenomena.

7. Means for synchronizing a pair of rotating devices comprising meansfor producin a pair of alternating current energies each having afrequency varying periodically between lower and upper limits and in adefinite integral relation to the number of revolutions of a differentone of said devices, means for mutually intermodulating said energies toproduce difference frequency energy, and further means for utilizingsaid difference frequency energy to control the speed of at least one ofsaid devices, whereby to restore and maintain the synchronism betweensaid devices.

8. Means for synchronizing a pair of rotating devices comprising meansfor producing a pair of alternating current electric energies eachhaving energy, and further means for utiliz-' a frequency varyinglinearly and periodically between lower and upper limits and within eachrevolution of a different one of said devices,

means for mutually intermodulating said energies to produce differencefrequency energy, and further means for utilizing said differencefrequency energy to control the speed of at least one of said devices,whereby to restore and maintain the synchronism between said devices.

9. Means for synchronizing a pair of rotatin devices comprising a pairof tone wheels each driven by one of said devices and having a varyingpitch between the teeth thereof to produce a pair of alternating currentelectric energies each having a frequency varying periodically betweenlower and upper limits and within each revolution of one of saiddevices, means for mutually intermodulating said energies to producedifference frequency energy, and further means for utilizing saiddifference frequency energy to control the speed of at least one of saiddevices, whereby to restore and maintain the synchronism between saiddevices.

10. Means for synchronizing a pair of rotating devices comprising meansfor producing a pair of alternating current electric energies eachhaving a frequency varying according to a saw-tooth curve between equallower and upper limits and within each revolution of a different one ofsaid devices, whereby to produce a pair of relatively wide and narrowbands of difference frequencies between said energies upon relativedeparture from synchronism of at least one of said devices, means forintermodulating said energie to produce difference frequency energy,filter means for segregating the energy of one of said differencefrequency bands from the output of said modulating means, a frequencydiscriminator for converting the segregated frequencies into energy ofcorresponding amplitude change, and means to control the speed of atleast one of said devices in accordance with the output of saiddiscriminator, whereby to restore and maintain the synchronism betweensaid devices.

11. Means for synchronizing a pair of rotating devices comprising meansfor producing a pair of alternating current electric energies eachhaving a frequency rising and falling substantially linearly betweendiiferent lower and upper limits and within each period of revolution ofa different one of said devices, whereby to produce a pai of relativelywide and narrow bands of difference frequencies between said energiesupon relative departure of one device from synchronism with the otherdevice, means for intermodulating said energies to produce differencefrequency energy, filter means for segregating from the modulationproduct control energy of said narrow band difference frequencies, adiscriminator for converting the segregated control energy into energyof corresponding amplitude changes, and means to control the speed of atleast one of said devices by the output of said discriminator, wherebyto restore and maintain the synchronism between said devices.

12. In a synchronizing system, a first rotating device, a secondrotating device, means for maintaining said second device at the samespeed and a constant relative phase with respect to said first devicecomprising means for producing a pair of alternating current electricenergies each having a frequency varying according to a sawtooth curvebetween equal lower and upper limits and within each revolution of adifferent one of said devices, whereby to produce a pair of relativelywide and narrow bands oi. difference frequencies between said energiesupon relative departure from synchronism of at least one of saiddevices, means for intermodulating said energies to produce differencefrequency energy. filter means for segregating the energy of one of saiddiiierence frequency bands from the output of said modulating means, afrequency discriminator for converting the segregated frequencies intoenergy of corresponding amplitude change, and means to control the speedof said second device in accordance with the output of saiddiscriminator, whereby to restore and maintain the synchronism betweensaid devices.

13. In a synchronizing system, a first rotating device, a secondrotating device, means for maintaining said second device at a constantspeed difference with respect to said first device comprising means forproducing a pair of alternating current electric energies each having afrequency rising and falling substantially linearly between diflerentlower and upper limits and within each period 01' revolution of adifferent one of said devices, whereby to produce a pair of relativeLvwide and narrow bands of diilerence frequencies between said energiesupon relative departure of one devic from synchronism with the otherdevice. means for intermodulatlng said encorresponding amplitudechanges, and means to control the speed of Said second device by theoutput of said discriminator, whereby to restore and maintain thesynchronism between said devices.

14. In a synchronizing system, a first periodic device having a firstfrequency, a second periodic device having a second frequency, means formaintaining said devices at the same frequency and a constant relativephase comprising means for deriving a pair of alternating currentenergies, each having a frequency varying periodically in definiteinteger relation to said first and ergies to produce diflerencefrequency energy,

filter means for segregating from the modulation product control energyof said narrow band difference frequencies. a discriminator forconverting the segregated control energy into energy 01' r secondfrequencies respectively, means for interinodulating said energies toproduce difference frequency energy, further means for producing controlenergy varying in amplitude in proportion to the frequency of saiddifierence frequency energy, and means utilizing said control energy tocontrol the frequency of said second device, whereby to restore andmaintain the synchrc nism between said devices.

MARCEL GABRIEL. GUSTAV GUANELLA.

REFERENCES CITED UNITED STATES PATENTS Name Date Number 1 Stoller et al.June 17, 1930

